WEST PALM BEACH, Fla. — Odds are, the red snapper on the menu is probably tilapia that’s striking a pose.

And a restaurant might say it serves white tuna, but not one sample recently tested in a study of seafood fraud in South Florida restaurants was white tuna. It was escolar — a fish banned in Japan and Italy and assigned warnings by the U.S. Food and Drug Administration because its natural toxins can cause diarrhea. White tuna is found only in a can. Fresh or frozen tuna may be marketed only as “tuna” or “albacore tuna,” according to FDA guidelines.

The study, conducted by the ocean conservation group Oceana, found that even though mislabelled seafood has been the frequent target of media exposes, federal prosecutions and state inspections, the problem persists and is widespread. DNA testing confirmed that nearly one-third of 96 seafood samples collected from 60 retail outlets, including groceries and restaurants, was mislabeled.

“I was definitely surprised by the findings,” said Kimberly Warner, senior scientist at Oceana, which has conducted similar studies in other metropolitan areas.

Warner used DNA testing to determine the true identify of fish samples gathered at restaurants from central Palm Beach County to Key West.

Of the 96 samples collected from 60 retail outlets, 40 were collected at grocery stores, 25 from restaurants and 31 from 15 sushi venues.

Sushi restaurants had the highest fraud rates, with 58 percent of the samples mislabeled. In grocery stores, the rate was only 8 percent.

One sample being sold in a restaurant as grouper was actually king mackerel, a high-mercury fish that carries a “do not eat” warning for young children and women who are pregnant or nursing.

Red snapper was mislabeled in six of the seven samples tested. Tilapia and other less expensive and less desirable fish were the most common substitutes.

Experts offer several reasons why the fraud continues despite years of headlines, laws punishing seafood fraud, and more than 1,400 citations issued in Florida alone since 2006. Profits are high, especially, and the populations of highly desirable fish, such as grouper, dwindle due to overfishing. At local grocery stores this week, the retail per-pound price of fresh grouper was $22.99. Grouper’s impersonator, tilapia, was $7.99 per pound.

Tracking the complex path from hook to plate has become more difficult as fish imports rise, experts say. About 86 percent of fish consumed in America is imported. The fraud can occur anywhere along the supply chain: commercial fishermen; processing and packaging plants; distributors; retailers; or restaurants and grocery stores.

Combine that with the unrefined palates and diets of most consumers and seafood fraud becomes easy. Americans ate 16 pounds of seafood on average in 2010, compared to 208 pounds of red meat and poultry.

“With fish it’s a lot easier (to deceive) simply because, for people who don’t eat much fish, it’s difficult for them to tell the difference between red snapper and other snapper,” said Dr. Mahmood Shivji, the director of the Guy Harvey Research Institute at Nova Southeastern University. “People are used to the texture of beef and chicken.”

Even Warner, who eats a lot of fish as part of her research, said she still has difficulty identifying some species — especially when they are covered in sauce. To prove how easy it is to defraud consumers, Oceana launched its Stop Seafood Fraud campaign in May 2011 with a seafood tasting for distributors, chefs and restaurateurs. After sampling vermilion snapper and tilapia prepared with the same sauce, the experts were asked to identify each fish. Many could not.

“People who play this fraud game bank on that,” Warner said.”

South Florida seafood fraud levels were actually lower than those found by Oceana in Los Angeles (55 percent) and Boston (48 percent). As part of its Stop Seafood Fraud campaign, Oceana is calling for increased inspections, prosecuting illegal fishing and improving food labels.